Roughly one in six people are affected by infertility worldwide and with more than half the world’s population now living in urban areas, researchers are interested in whether living in noisy and polluted cities could be to blame.

A new study in Denmark has used nationwide data to explore infertility.

It found long-term exposure to air pollution and traffic noise may be associated with higher infertility – but these factors affect men and women differently.

What do pollution and noise do to the body?

We know traffic pollution has undeniable impacts on the environment. Its negative effects on human health are also well established, with links to cancers and heart disease.

Inhaled chemicals from polluted air may also travel to the reproductive tract via the blood. They can reduce fertility by either disrupting hormones or causing direct damage to eggs and sperm.

The effects of traffic noise on health are less clear, but some research suggests this affects stress hormones, which could alter fertility.

What did they look at?

This new study was conducted in Denmark, which collects data about every resident into multiple national databases over their lifetime, using a unique identification number.

Nationwide data allows researchers to investigate links between a person’s health and factors such as where they live, their job, education history and family. This method is called “data linkage”.

The study aimed to capture people who were likely to be trying to get pregnant, and therefore at risk of receiving an infertility diagnosis.

Over 2 million men and women were identified as being of reproductive age. The study looked at those who were:

• aged 30 – 45
• living together or married
• with less than two children
• living in Denmark between January 1 2000 and December 31 2017.

It excluded anyone who was diagnosed with infertility before age 30, lived alone or in a registered same-sex partnership. People with incomplete information (like a missing address) were also excluded.

There were 377,850 women and 526,056 men who fit these criteria.

The study did not survey them. Instead, over a five-year period it cross-checked detailed information about where they lived and whether they received an infertility diagnosis, collected from the Danish National Patient Register.

Researchers also estimated how much each residential address was exposed to road traffic noise (measured in decibels) and air pollution, or how much fine particulate matter (called PM2.5) is in the air.

What did they find?

Infertility was diagnosed in 16,172 men (out of 526,056) and 22,672 women (out of 377,850).

The study found the risk of infertility was 24% greater for men exposed to PM2.5 levels 1.6 times higher than recommended by the World Health Organization.

For women, exposure to traffic noise at 10.2 decibels higher than average (55-60 decibels) was associated with 14% increased infertility risk for those over 35.

Risks were similar based on residing in urban or rural areas, and when accounting for education and income.

What does it suggest?

The study highlights how environmental exposure can have immediate and long-term effects, and may affect male and female reproduction differently.

After puberty, men constantly produce sperm – up to 300 million a day. The impact of environmental changes on male fertility – such as exposure to toxic pollutants — tends to show up more quickly than in females, affecting sperm number and quality.

In contrast, women are born with all their eggs, and cannot produce new ones. Eggs have some “damage control” mechanisms to protect them from environmental hazards across a lifetime.

This doesn’t mean eggs are not sensitive to damage. However it may take longer than the five years of exposure this study looked at for the impact on women to become clear.

It is possible even longer-term studies could reveal a similar impact for pollution on women.

Is data linkage a good way to look at fertility?

Data linkage can be a powerful tool to uncover links between environmental exposures and health. This allows assessments in large numbers of people, over long periods of time, like this recent Danish study.

But there are inherent limitations to these types of studies. Without surveying individuals or looking at biological factors – like hormone levels and body mass — the research relies on some assumptions.

For example, this study involved some major assumptions about whether or not couples were actually trying to conceive.

It also calculated people’s exposure to noise and air pollution according to their address, assuming they were at home.

A more precise picture could be painted if information was gathered from individuals about their exposure and experiences, including with fertility.

For example, surveys could include factors like sleep disturbance and stress, which can alter hormone responses and impact fertility. Exposure to chemicals that disrupt hormones is also found at home, in everyday household and in personal care products.

In its scale, this study is unprecedented and a useful step in exploring the potential link between air pollution, traffic noise and infertility. However more controlled studies – involving actual measures of exposure instead of estimations – would be needed to deepen our understanding of how these factors affect men and women.

Amy L. Winship, Group Leader and Senior Research Fellow, Anatomy and Developmental Biology, Monash University and Mark Green, Merck Serono Senior Lecturer in Reproductive Biology, The University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Wellington:

We hear a lot about women’s biological clock and how age affects the chance of pregnancy.

New research shows men’s fertility is also affected by age. When dads are over 50, the risk of pregnancy complications increases.

Data from more than 46 million births in the United States between 2011 and 2022 compared fathers in their 30s with fathers in their 50s.

While taking into account the age of the mother and other factors known to affect pregnancy outcomes, the researchers found every ten-year increase in paternal age was linked to more complications.

The researchers found that compared to couples where the father was aged 30–39, for couples where the dad was in his 50s, there was a:

• 16% increased risk of preterm birth
• 14% increased risk of low birth weight
• 13% increase in gestational diabetes.

The older fathers were also twice as likely to have used assisted reproductive technology, including IVF, to conceive than their younger counterparts.

Dads are getting older

In this US study, the mean age of all fathers increased from 30.8 years in 2011 to 32.1 years in 2022.

In that same period, the proportion of men aged 50 years or older fathering a child increased from 1.1% to 1.3%.

We don’t know the proportion of men over 50 years who father children in Australia, but data shows the average age of fathers has increased.

In 1975 the median age of Australian dads was 28.6 years. This jumped to 33.7 years in 2022.

How male age affects getting pregnant

As we know from media reports of celebrity dads, men produce sperm from puberty throughout life and can father children well into old age.

However, there is a noticeable decline in sperm quality from about age 40.

Female partners of older men take longer to achieve pregnancy than those with younger partners.

A study of the effect of male age on time to pregnancy showed women with male partners aged 45 or older were almost five times more likely to take more than a year to conceive compared to those with partners aged 25 or under. More than three quarters (76.8%) of men under the age of 25 years impregnated their female partners within six months, compared with just over half (52.9%) of men over the age of 45.

Pooled data from ten studies showed that partners of older men are also more likely to experience miscarriage. Compared to couples where the male was aged 25 to 29 years, paternal age over 45 years increased the risk of miscarriage by 43%.

Older men are more likely to need IVF

Outcomes of assisted reproductive technology, such as IVF, are also influenced by the age of the male partner.

A review of studies in couples using assisted reproductive technologies found paternal age under 40 years reduced the risk of miscarriage by about 25% compared to couples with men aged over 40.

Having a male under 40 years also almost doubled the chance of a live birth per treatment cycle. With a man over 40, 17.6% of treatment rounds resulted in a live birth, compared to 28.4% when the male was under 40.

How does male age affect the health outcomes of children?

As a result of age-related changes in sperm DNA, the children of older fathers have increased risk of a number of conditions. Autism, schizophrenia, bipolar disorders and leukaemia have been linked to the father’s advanced years.

A review of studies assessing the impact of advanced paternal age reported that children of older fathers have increased rates of psychiatric disease and behavioural impairments.

But while the increased risk of adverse health outcomes linked to older paternal age is real, the magnitude of the effect is modest. It’s important to remember that an increase in a very small risk is still a small risk and most children of older fathers are born healthy and develop well.

Improving your health can improve your fertility

In addition to the effects of older age, some chronic conditions that affect fertility and reproductive outcomes become more common as men get older. They include obesity and diabetes which affect sperm quality by lowering testosterone levels.

While we can’t change our age, some lifestyle factors that increase the risk of pregnancy complications and reduce fertility, can be tackled. They include:

Get the facts about the male biological clock

Research shows men want children as much as women do. And most men want at least two children.

Yet most men lack knowledge about the limitations of female and male fertility and overestimate the chance of getting pregnant, with and without assisted reproductive technologies.

We need better public education, starting at school, to improve awareness of the impact of male and female age on reproductive outcomes and help people have healthy babies.

For men wanting to improve their chance of conceiving, the government-funded sites Healthy Male and Your Fertility are a good place to start. These offer evidence-based and accessible information about reproductive health, and tips to improve your reproductive health and give your children the best start in life.

(Author:Karin Hammarberg, Senior Research Fellow, Global and Women’s Health, School of Public Health & Preventive Medicine, Monash University)

(Disclosure Statement:Karin Hammarberg works for the Victorian Assisted Reproductive Treatment Authority which manages the Your Fertility program)

This article is republished from The Conversation under a Creative Commons license. Read the original article.
 

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